1. Field of the Invention
The invention relates to variable pitch propellers whose blades are mounted in a hub for rotation about their longitudinal axes, the ends of the blades entering the hub being provided with a crown or ring of peripheral teeth which mesh with axially slidable racks lying at the center of the hub.
2. Description of the Prior Art
Smaller sports airplanes and powered gliders have almost without exception air screws as a means of propulsion, both puller propellers and pressure propellers being used. Such propeller aircraft are being used in ever increasing numbers, and for aeronautic and not least for economic reasons it is desirable to have propellers with adjustable blades. As is well known, variable pitch propellers present the advantage that the pitch of the propeller blades can be set according to each phase of flight, such as taking off, rising, travelling flight or coasting (gliding); it being also possible to preselect a braking attitude for landing. The variable pitch propellers that are commercially available at present are, however, of very complex design and correspondingly expensive. They are, moreover, conceived for larger and more powerful aircraft and for the already stated reasons cannot be considered for inexpensive, light sports airplanes.
Variable pitch propellers of the type mentioned at the outset are already known wherein the adjustability of the blades is achieved by comparatively simple means. The designs in question, however, suffer from the drawback that they may involve, owing to the finishing tolerances, either enhanced flank play between the rack and the tooth crown or mutual jamming of the two parts. Either is equally disadvantageous and indeed may be disastrous. If the tooth flank play is too great the propeller blade will not keep the exact set pitch, or, in some circumstances, the blade may start fluttering, which is deleterious from the point of view of flow dynamics. Mutual jamming of the tooth crown and rack makes adjustment impossible.